Solution-based Synthesis And Optical Properties Investigation Of Rare-earth Doped Fluoride Upconversion Microcrystals/Nanocrystals

Lanthanide-doped luminescent nanomaterials have great potentials in the fields ofthree-dimension displays, optical devices, biosensors and anti-counterfeiting applications.Particularly, the use of lanthanide-doped upconversion （UC） nanomaterials as biolabels forsensitive biological detection has attracted considerable interests due to their unique opticalproperties. Recently, fluorides have been used as an attractive host for phosphors withinteresting UC luminescent properties because of their high UC efficiency and excellentchemical stability. Establishing well-controlled synthetic strategies to these materials,understanding their growth and luminescent mechanisms, and the relationships of theirstructures, morphologies and optical behaviors, are crucial to the production ofnanomaterials with designated optical properties.Lanthanide-doped NaGdF4UC nanocrystals （NCs） with good crystallinity,contrallable morphologies and uniform size were prepared in water-ethanol-oleic acid-sodium oleate system via a facile wet chemistry strategy. Multicolor UC luminescenceswere achieved in NaGdF4NCs through control of different combinations of lanthanidedopants and dopant concentration, which are promising for the applications of multiplebiolabels. The results indicate that this work provides a new way for the preparation ofhigh quality fluoride NCs.A series of MF₂:Yb³⁺/Er³⁺(Tm³⁺)（M=Ca, Sr, Ba） UC NCs were synthesized byhydrothermal method in water-ethanol-oleic acid-sodium oleate system. The effects ofexperimental conditions on the morphology and structure of MF₂:Yb³⁺/Er³⁺NCs wereinvestigated, and the optical properties and characteristics of structure of the as-preparedsamples also have been measured. Using SrF₂:Yb³⁺/Er³⁺as a model, the effect of differentsurfactants on the morphologies and optical behaviors of MF₂:Yb³⁺/Er³⁺NCs wereinvestigated, and structural and kinetic factors governing the anisotropic growth tendencyand shape evolutions on nanoscale under hydrothermal environment are systematicallystudied.In modified water-ethanol-oleic acid system, BaYF5:Yb³⁺/Er³⁺UC NCs with tunablesizes were prepared by adjusting experiment conditions. The surface effect andsize-dependent UC luminescence behaviors have been observed in BaYF5:Yb³⁺/Er³⁺NCs.In addition, BaYF5:Yb³⁺/Er³⁺UC materials have been synthesized via a surfactant-freeaqueous solution rout. Different morphologies and structure can be controlled by varying the different fluorine sources, temperature and reaction time. More importantly, therelationships of their structures, morphologies and optical behaviors have been discussed.